Resinous compositions having improved processability and gas permeation resistance and molded structures thereof

ABSTRACT

A resinous composition excellent in processability and gas permeation resistance, which comprises (A) 30 to 98 % by weight of a crystalline polyolefin, (B) 2 to 70 % by weight of a saponified product of an ethylene-vinyl acetate copolymer having an ethylene content of 25 to 75 mole % and a degree of saponification of at least 93 %, and (C) 0.5 to 15 parts by weight, per 100 parts by weight of said polyolefin and ethylenevinyl acetate copolymer saponified product, of a thermoplastic polymer containing a carbonyl group in the main or side chain thereof, and a molded structure formed therefrom, which has a specific multi-layer structure and a high gas permeation resistance.

United States Patent Hirata et a1.

[ Dec. 31, 1974 Filed: June 12, 1972 Appl. N0.: 261,804

Assignee:

Foreign Application Priority Data June 18, 1971 Japan 4643356 Jan. 4,1972 Japan 47-5810 US. Cl 161/227, 161/190, 161/231, 161/255, 161/253,161/254, 260/857 L, 260/859, 260/873, 260/897 B, 264/176,

Int. Cl 13321) 27/08, C08g 41/04 Field of Search..... 260/857 L, 897 B;161/252,

References Cited UNITED STATES PATENTS 1/1963 Fior et a1 260/857 L5/1965 Rees 260/897 B 8/ 1968 Kirk et a1. 260/897 B 12/1968 Chiba et a1260/897 B 111969 Maloney 260/897 B l 1/1970 Gorton et a1 260/897 B3,615,106 10/1971 Flanagan et a1 260/897 B 3,639,502 l/l972 Okazaki etal. 260/857 L 3,663,663 5/1972 McAda 260/897 B 3,700,751 10/ 1972Mueller et al 260/857 L FOREIGN PATENTS OR APPLICATIONS 1,950,479 5/1970Germany 1,254,354 11/1971 Great Britain OTHER PUBLICATIONS ChemicalAbstracts, 75:6914w, (Soki), Japan, 70,31,758.

[5 7] ABSTRACT A resinous composition excellent in processability andgas permeation resistance, which comprises (A) to 98 by weight of acrystalline polyolefin, (B) 2 to by weight of a saponified product of anethylenevinyl acetate copolymer having an ethylene content of 25 to moleand a degree of saponification of at least 93 and (C) 0.5 to 15 parts byweight, per parts by weight of said polyolefin and ethylene-vinylacetate copolymer saponified product, of a thermoplastic polymercontaining a carbonyl group in the main or side chain thereof, and amolded structure formed therefrom, which has a specific multi-layerstructure and a high gas permeation resistance.

20 Claims, 8 Drawing Figures PATENTED 3. 857. 754

sum 1 [IF 4 PATENTEDDECB' 3,857, 754

SHEET 2 OF 4 I00 Fly. 3

g z a 9 E m Z E I 5 T WAVE LENGTH (cm") Hg. 4

[LOg /I /F] 5o O l I 50 CONCENTRATION OF SAPONIFIED PRODUCT (wt /o)PATENIEU-DEDSI I974 3, 857, 754

' SHEET 3 OF 4 I 1 I I I 1 l I I400 I200 I000 800 Fig.5

3200 124002000 A |8OO' WAVE LENGTH I I I I l O O O o o O m 1 01TRANSMISSION RESINOUS COMPOSITIONS HAVING IMPROVED PROCESSABILITY ANDGAS PERMEATION RESISTANCE AND MOLDED STRUCTURES THEREOF This inventionrelates to a novel resinous composition being excellent inprocessability and gas permeation resistance and a molded structurethereof. More particularly, the invention relates to a resinouscomposition having improved processability and gas permeation resistancewhich comprises a blend ofa polyolefin, especially a low densitypolyethylene, a saponified product of an ethylene-vinyl acetatecopolymer and a carbonyl group-containing thermoplastic polymer, and amolded structure of such resinous composition. More detailedly, theinvention relates to a molded article having a structure characterizedby a novel layer distribution, which is formed from a molten mixturecomprising a polyolefin, a saponified product of an ethylenevinylacetate copolymer and a carbonyl groupcontaining thermoplastic polymer,especially a molded article such as film, sheet, container or tube astructure of a novel layer distribution excellent in gas permeationresistance.

Polyolefins have heretofore been broadly used as packaging materials forfoodstuffs and the like by reason of excellent mechanical strength andsanitary characteristics. However, polyolefins are fatally defective inthat permeability of gases such as oxygen and carbon dioxide gas is veryhigh, and polyolefins are still insufficient in that foodstuffs cannotbe preserved for a long time with use of containers or the like formedof polyolefins.

In order to improve the gas permeation resistance in polyolefins methodshave been proposed to copolymerize ethylene with various vinyl monomers.For instance, US. Pat. No. 3,419,654 discloses the use of a saponifiedproduct of an ethylene-vinyl acetate copolymer. Although such saponifiedproduct is advantageous over polyolefins in the point that its oxygenpermeability is much smaller than that of polyolefins, it is stilldefective in that its water vapor permeability is high because of itshydrophilic properties and that its mechanical strength, especiallyimpact resistance, is considerably low.

We have now found that when an ethylene-vinyl acetate copolymersaponified product and a polyolefin such as low density polyethylene,each having the defects such as mentioned above, are blended at aspecific ratio which will be detailed hereinbelow, there can be obtaineda resinous composition in which permeability of ordinary gases such asoxygen, water vapor and carbon dioxide gas is extremely low and which isexcellent in mechanical properties such as impact resistance andphysical properties such as transparency, and that when a specificamount of a carbonyl group-containing thermoplastic polymer isincorporated in such resinous composition, the processability of thecomposition at the molding operation can be highly improved while theabove-mentioned characteristic properties are retained, and theresulting molded article is highly improved in surface smoothness anduniformity.

It has also been found that when the abovementioned polyolefin,ethylene-vinyl acetate copolymer saponified product and carbonylgroup-containing thermoplastic polymer are melt-blended at specificratios which will be explained hereinbelow and the molten mixture isextruded and molded under such specific'extrusion conditions that thedifference between the average flow rate of the polyolefin melt and theaverage flow rate of the ethylene-vinyl acetate copolymer saponifiedproduct is at least I cm/sec, there can be obtained a molded structurein which the polymer composition is different in the thickness directionbut substantially identical in the plane direction and which has a layerstructure wherein layers are continuous with respect to the planedirection; in such structure, there are formed layers containing theethylene-vinyl acetate copolymer saponified product at a ratio exceedingthe average content and layers containing the polyolefin at a ratioexceeding the average content, and by reason of such specific layerstructure, the molded structure exhibits an extremely low permeabilityof ordinary gases such as oxygen, water vapor and carbon dioxide gas andis excellent in mechanical properties such as stiffness and impactresistance and physical properties such as transparency; and that inpreparation of such molded structure, when a specific amount of acarbonyl group-containing thermoplastic polymer is added to theabove-mentioned polyolefin and ethylene-vinyl acetate copolymersaponified product, the surface smoothness and uniformity of the moldedstructure can be highly improved while the above-mentioned desirableproperties are retained as they are, and the processability of thecomposition at the molding operation can be highly improved.

In the instant specification, it is defined that in a hollow moldedstructure, the plane direction means the peripheral direction of thestructure and the thickness direction means the direction vertical tosaid plane direction, namely the radial direction.

Accordingly, an object of this invention is to provide a novel resinouscomposition which has an excellent gas permeation resistance similarlyagainst oxygen, water vapor, carbon dioxide gas, etc. and which isexcellent in mechanical properties such as impact resistance, softnessand toughness, physical properties such as transparency, andprocessability, especially melt-molclability Another object of thisinvention is to provide a novel resinous composition which can readilybe molten and extrusion-molded into films, containers and others moldedarticles and which can give a molded resin article excellent in thesurface smoothness and uniformity.

A further object of this invention is to provide a molding resinouscomposition which can be suitably used for formation of packagingmaterials for foodstuffs or the like, such as films, bags, bottles andtubes.

Still another object of this invention is to provide a molded structureof a novel layer structure which exhibits an excellent gas permeationresistance similarly against oxygen, water vapor, carbon dioxide gas,etc. and which is excellent in mechanical properties such as stiffnessand impact resistance.

A still further object of this invention is to provide a novel moldedstructure which has a layer structure in which the polymer compositionis different in the thickness direction but substantially identical inthe plane direction and layers are continuous with respect to the planedirection, in spite of the fact that the molded structure is formed froma molten mixture comprising a polyolefin and a saponified product of anethylene vinyl acetate copolymer.

A still further object of this invention is to provide a moldedstructure having a novel layer structure comprising layers containing asaponified product of an ethylene-vinyl acetate copolymer at a ratioexceeding the average content, and layers containing a polyolefin at aratio exceeding the average content, wherein every two adjacent layersare bonded to each other without any intermediate bonding layer of anadhesive.

A still further object of this invention is to provide a molding methodaccording to which a molded structure of the above-mentioned novel layerstructure can readily be prepared by only one extrusion moldingapparatus.

In accordance with this invention, there is provided a resinouscomposition excellent in processability and gas permeation resistance,which consists essentially of (A) 30 to 98% by weight of a crystallinepolyolefin, particularly a low density polyethylene having a density ofless than 0.929 g/cc, especially less than 0.928 g/cc, (B) 2 to 70% byweight of a saponified product of an ethylene-vinyl acetate copolymerhaving an ethylene content of 25 to 75 mole percent and a degree ofsaponification of at least 93%, and (C) 0.5 to 15 parts by weight, per100 parts by weight of the sum of said crystalline polyolefin and saidethylene-vinyl acetate copolymer saponified product, of a thermoplasticpolymer containing a carbonyl group in its main or side chain.

In accordance with one preferable embodiment of this invention, there isprovided a molded structure formed from a molten mixture containing (A)a polyolefin and (B) a saponified product of an ethylene-vinyl acetatecopolymer having an ethylene content of 25 to 50 mole percent and adegree of saponification of at least 96% at a weight ratio of A Branging from 95 5 to 75 :25, and (C) 0.5 to parts by weight, per 100parts by weight of the sum of said polyolefin and said ethylene-vinylacetate copolymer saponified product, of a thermoplastic polymercontaining a carbonyl group in its main or side chain, said moldedstructure having a layer structure in which the polymer composition isdifferent in the thickness direction but substantially identical in theplane direction and every two adjacent layers are bonded to each otherwithout any intermediate bonding layers of an adhesive, wherein whensaid molded structure is divided in three layers in the thicknessdirection, at least one layer contains the ethylene-vinyl acetatecopolymer saponified product in an amount expressed by the followingformula wherein X is the average (percent by weight) of theethylene-vinyl acetate copolymer saponified product in said moldedstructure, m is a number of from 1.2 to 4, and M, is the content(percent by weight; which is sometimes called concentration) of theethylene-vinyl acetate copolymer saponiffied product in said layer, andat least one layer contains the ethylene-vinyl acetate copolymersaponified product in amount expressed by the formula M2 "12X wherein Xis as defined above, m is a number of from 0 to 0.9, and M is thecontent (percent by weight) of the ethylene-vinyl acetate copolymersaponified product in said layer. This invention will now be illustratedmore detailedly. Resinous Composition The saponified product of anethylene-vinyl acetate copolymer to be used in the molded structure ofthis invention is obtained by saponifying an ethylenevinyl acetatecopolymer having an ethylene content of 25 to mole percent so that thedegree of saponification reaches at least 93%, especially at least 96%.In case the ethylene content exceeds 75 mole percent in the saponifiedcopolymer, the gas permeation resistance (gas-barrier property) againstgases such as oxygen is lost, and the objects of this invention cannotbe attained. In case the ethylene content of the saponified copolymer isless than 25 mole percent, the composition exhibits a high hydrophilicproperty and its water vapor permeability becomes high with degradationof its moldability. Accordingly, use of such saponified co-' polymer isnot suitable for attaining the objects of this invention.

In order for the molded structure to have an improved gas permeationresistance, it is essential that the degree of saponification should beat least 93%, espe cially at least 96%.

A saponified product of an ethylene-vinyl acetate copolymer to beespecially preferably used in this invention has an ethylene content of25 to 50 mole percent and a degree of saponification of at least 99%.

The molecular weight of the ethylene-vinyl acetate copolymer saponifiedproduct to be used in this invention is not particularly critical, asfar as it is in general within the range capable of forming films. Ingeneral, the viscosity of the ethylene-vinyl acetate copolymer saponfiedproduct is measured with use of a mixed solvent of by weight of phenoland 15% by weight of water. In this invention, it is preferred that theethylenevinyl acetate copolymer saponified product used has an intrinsicviscosity (1;), measured, at 30C. in such mixed solvent, of from 0.07 to0.17 l/g. In the case of a saponified copolymer having an intrinsicviscosity (1 of lower than 0.07 l/g, the mechanical strength of thefinal molded article is insufficient, and in the case of a saponifiedcopolymer having an intrinsic viscosity (n) exceeding 0.17 l/g, themoldability of the resulting resinous composition tends to be lowered.

In this invention, selection of a polyolefin among various thermoplasticresins and formation of a molten mixture by combining so selectedpolyolefin with an ethylene-vinyl acetate copolymer saponified productare very important for improving the gas permeation resistance in thefinal molded structure and for obtaining a molded structure having theabove-mentioned specific layer structure. According to this invention,the use of this combination of the polyolefin and saponified copolymerresults in a molded structure having an excellent gas permeationresistance sim larly against all of ordinary gases such as oxygen, watervapor and carbon dioxide gas and excellent physical properties such asgood stiffness, high impact resistance and high transparency.

Any of polyolefins which have heretofore been used for molding of filmsor containers and the like broadly in the art may be used as thepolyolefin in this invention. As such polyolefin, there may be employedhomopolymers and copolymers of olefins expressed by the followingformula CHg=CH wherein R is a hydrogen atom or an alkyl group having upto 4 carbon atoms.

In order to obtain a molded article having sufficient mechanicalstrength from such polyolefin, it is essential that the olefinhomopolymer or copolymer should be crystalline. As such crystallinepolyolefin there may be mentioned, for instance, low densitypolypentanemedium density polyethylene, high density polyethylene,isotactic polypropylene, crystalline ethylenepropylene copolymer,polybutene- 1 and polypentencel. Ofcourse, in this inve ntion thepolyolefin to be used is not limited to olefin homopolymers andcopolymers of two or more olefins, but copolymers comprising a smallamount, for instance, up to 5 mole percent, of other ethylenicallyunsaturated comonomer with a range such as will not substantially damagethe properties of the polyolefin, may be used. As such comonomercomponent, there may be exemplified vinyl chloride, vinyl acetate,acrylic acid, esters thereof, methacrylic acid and esters thereof.

In general, the molecular weight of the polyolefin is not particularlycritical in this invention, as far as it is within the film-formingrange. For instance, a polyolefin having an average molecular weight offrom 5,000 to 400,000 (corresponding to a melt index, MI (measuredaccording to ASTM 1238) from 0.05 to 5.0 g/ min) is used preferably ingeneral.

Polyolefins to be preferably used in this invention are, expressed inthe order of importance, (I) a low density polyethylene having a densityof from 0.917 to 929 g/cc, (II) a medium density polyethylene having adensity of from 0.930 to 0.939 g/cc, (III) a high density polyethylenehaving a density of at least 0.940 g/cc, and (IV) an isotacticpolypropylene.

In this invention, the use of a low density polyethylene having adensity of less than 0.929 g/cc is especially preferred. Morespecifically, in accordance with a preferable embodiment of thisinvention, a low density polyethylene is especially selected amongvarious thermoplastic resins and combined with a carbonylgroupcontaining polymer, and by a simple operation of blending thiscombination of the low density polyethyleneand carbonyl group-containingpolymer with a saponified product of an ethylene-vinyl acetatecopolymet, there can readily be obtained a composition having a desiredcombination of high gas permeation resistance, high impact resistanceand high transparency. It is important that the low density polyethyleneto be used in the composition of the above preferable embodiment of thisinvention should have a density of less than 0.929 g/cc. Otherpolyethylenes having a density of greater than 0.929 g/cc, for instance,medium pressure process polyethylenes or low pressure polyethylenes(high density polyethylenes), have a tendency to give, in general, apoor transparency when blended with an ethylene-vinyl acetate copolymersaponified product. Further, a vessel or container molded from aresinous composition comprising such polyethylene is inferior insoftness characteristics such as squeezing property. Of course, in thisinvention, in preparing containers of which transparency is not requiredor containers of which a rigid property is required, it is possible toemploy medium density polyethylene, high density polyethylene andisotactic polypropylene.

In this invention, when combination of a polyolefin, especially a lowdensity polyethylene with the said saponified ethylene-vinyl acetatecopolymer is used, by

employing the molding procedures which will be detailed hereinbelow, itis made possible to manifest very prominently the characteristic featurein the molded structure of this invention, that is, the feature of thespecific layer structure constructed of layers differring from eachother in the resin composition, and to improve such properties as gaspermeation resistance, transparency, and impact resistance greatly.

It has been disclosed in the specification of Japanese PatentPublication No. 31758/ that when a saponified product of anethylene-vinyl acetate copolymer is blended with anacrylonitrile-butadiene copolymer, the impact resistance of thesaponified ethylene-vinyl acetate copolymer is improved. However, thespecification of said Japanese Patent Publication clearly teaches thatsince there is no complete compatibility between the ethylene-vinylacetate copolymer saponified product and acrylonitrile-butadienecopolymer, the resulting resinous blend is semi-transparent. Thus, it isshown that this resinous composition has a defect with respect totransparency.

It may be considered to blend an ethylene-vinyl acetate copolymersaponified product with other rubbery polymer such, for example, as anethlene-propylene copolymer, a polyisobutylene, a chlorosulfonatedpolyethylene, a polyisoprene, a polysulfurized rubber, a polychloropreneor a styrene-butadiene copolymer.

Attempts to obtain a resinous composition excellent in gas permeationresistance, impact resistance and transparency by graft or blockpolymerizing an ethylene-vinyl acetate copolymer saponfied product withother monomer or polymer have been known. For instance, thespecification of Japanese Patent Publication No. 3275/70 teaches thatwhen e-caprolactam is added to a saponified product of an ethylene-vinylacetate copolymer and the mixture is polymerized under heat, there isobtained a blocked, grafted or partially cross-linked product composedof combined saponified copolymer and poly-e-caprolactam and that theabovementioned characteristics are improved in the resulting resinousproduct. Further, in Chemical Abstracts, vol. 73 (1970), 15729 a, it isdisclosed that when a high density polyethylene not masticated afterpolymerization and a saponified product of an ethylene-vinyl acetatecopolymer are kneaded together with a freeradical-forming catalyst underheat and pressure to form a block-graft copolymer, there is obtained aproduct excellent in gas permeation resistance, anti-stresscrackingproperty and resistance against thermal shrinkage.

However, each of these known techniques is industrially and economicallydisadvantageous in that special operations and materials are requiredfor accomplishing the block or graft copolymerization, and each ofresinous compositions obtained according to such known techniques cannotescape from a defect of degradation in moldability because thecross-linked structure should inevitably be introduced at the block orgraft copolymerization.

In contrast to these known techniques, when a low density polyethyleneis used and coupled with a carbonyl group-containing polymer, a moldedstructure having the above-mentioned desired combination of excellentgas permeation resistance, impact resistance and transparency can beobtained merely by blending, melting and molding. Further, themelt-extrusion molding of the resinous blend can be accomplished veryeasily, with high improvement of the surface smoothness and uniformityin the resulting molded structure. This feature is quite unobvious andunexpected from the conventional knowledge that in case polyolefin isused in combination with a saponified product of an ethylene-vinylacetate copolymer, it is necessary to perform the blockandgraft-copolymerization between both polymer.

Of course, in a molded product of the abovementioned specificmulti-layer structure according to this invention, it is possible toimprove mechanical properties such as stiffness, tensile strength andtear strength by employing high density polyethylene or isotacticpolypropylene.

In the resinous composition of this invention, it is especiallyimportant that 30 to 98% by weight of a crystalline polyolefin,especially a low density polyethylene such as mentioned above, is mixedwith 2 to 70% by weight of a saponified product of an ethylene-vinylacetate copolymer. From the experimental data shown in Examples givenhcreinbelow, it can readily be understood that by employing apolyolefin, especially a low density polyethylene, and a saponifiedproduct of an ethylene-vinyl acetate copolymer at the above specificratio specified in this invention, it is possible to maintain apermeability of oxygen or carbon dioxide gas at a level much lower thanthe level attained by the single use of the polyolefin, and at the sametime, the water vapor permeability is about one-tenth of the water vaporpermeability observed when the saponified ethylene-vinyl acetatecopolymer alone is used. Still further, as compared with the case of thesingle use of the saponified ethylene-vinyl acetate copolymer, theimpact resistance can be highly improved by the use of the abovecombination of the polyolefin and saponified ethylene-vinyl acetatecopolymer.

Moreover, by adjusting the mixing ratio of the polyolefln and saponifiedethylene-vinyl acetate copolymer within the above-mentioned range, it ismade possible to improve the physical properties such as toughness andsoftness very highly, as compared with the single use of the saponifiedethylene-vinyl acetate copolymer.

The resinous composition of this invention comprises, in addition to theabove polyolefin and saponified ethylene-vinyl acetate copolymer, athermoplastic polymer containing a carbonyl group in the main or sidechain in amount of 0.5 to parts by weight per 100 parts of the sum ofthe polyolefin and saponified copolymer. Incorporation of this carbonylgroupcontaining thermoplastic polymer improves not only the surfacesmoothness and uniformity of the resulting molded structure but also theprocessability and workability of the composition at the moldingoperation.

As such carbonyl group-containing thermoplastic polymer, there mayoptionally be employed any of thermoplastic polymers containing in themain or side chain carbonyl groups from free carboxylic acids,carboxylic acid salts, carboxylic acid esters, carboxylic anhydrides,carboxylic acid amides, carbonic acid esters, urethane and urea.Examples of such polymer will now be described.

a. Homopolymers or copolymers of monomers expressed by the followingformula (I), and copolymers of monomers expressed by the formula (I)with olefins such as ethylene and propylene or other vinyl monomers suchas styrene, vinyl chloride, vinyl acetate and acrylonitrile:

wherein R is a hydrogen atom or a lower alkyl group having up to 4carbon atoms, and R is a hydrogen atom or an alkyl group having I to 12carbon atoms.

Specific examples of the polymer of this type are polyacrylic acidesters, polymethacrylic acid esters, ethylene/acrylic acid estercopolymers, acrylic acid ester/acrylic acid copolymer, ethylene/acrylicacid ester- /acrylic acid copolymers, ethylene/acrylic acid copolymers,styrene/methacrylic acid ester/acrylic acid copolymers, acrylic acidester/vinyl chloride copolymers, methacrylic acid ester/vinyl chloridecopolymers, styrene/methacrylic acid ester/butadiene copolymers, andmethacrylic acid esters/acrylonitrile copolymers.

b. Homopolymers or copolymers of vinyl esters expressed by the followingformula (II), and copolymers of monomers expressed by the formula (ll)with olefins such as ethylene or other group-free vinyl monomers:

H) (II) wherein R is a hydrogen atom or an alkyl or phenyl group.

Specific examples of the polymer of this type are polyvinyl acetate, apolyvinyl propionate, ethylene/vinyl acetate copolymers, acrylic acidester/vinyl acetate copolymers, and vinyl chloride/vinyl acetatecopolymers.

c. lonomers, that is, resins obtained by neutralizing copolymers ofolefins with unsaturated carboxylic acids and optionally other vinylmonomers, with an alkali metal, an alkaline earth metal, zinc or anorganic base.

Specific examples of the polymer of this type are Surlyns marketed by E.I. du' Pont de Nemours & Co., U.S.A.

d. Copolymers of maleic anhydride with other vinyl monomers.

Specific examples of the polymer of this type are maleic anhydride/vinylether copolymers, and maleic anhydride/vinyl chloride copolymers.

e. Polyamides composed of the recurring units expressed by the formulapoly-w-aminocaprylic acid, polywterephthalate/isophthalate. acid,poly-waminodecanoic acid, poly-m-aminoundecanoic acid,poly-m-aminotridecanoic acid, polyhexamethylene adipamide,polyhexamethylene sebacamide, polyhexawherein R is an alkylene group of2 to 6 carbon atoms, and R is an alkylene or arylene group of 2 to 24carbon atoms. Specific examples of the polymer of this type arepolyethylene adipate, polethylene sebacate, polyethylene terephthalate,polytetramethylene isophthalate, 3

and polyethylene tetrephthalate/isophthalate.

g. Polyureas composed of the recurring units expressed by the formula Ki r wherein R and R stand for an alkylene group of l to 13 carbon atoms.

Specific examples of the polymer of this type are polyhexamethyleneurea,polyheptamethyleneurea, polyundecamethyleneurea andpolynonamethyleneurea.

h. Polyurethanes or polyureaurethanes expressed by the formula wherein Ris an alkylene group of 3 to 24 carbon atoms, or a polyether orpolyester residue, R is an alkylene or arylene group of 3 to 24 carbonatoms, R is an alkylene or arylene group of 1 to 13 carbon atoms, and kis 0 or 1.

Specific examples of the polymer of this type arepolytetramethylenehexamethylene, polyhexamethylenetetramethylenethane,and polyurethanes formed by chain-extending isocyanate-terminatedpolyesters or polyethers with a diamine or water.

i. Polycarbonates composed of the recurring units expressed by theformula wherein R is a hydrocarbon group of 8 to 15 carbon atoms.

Specific examples of the polymer of this group are poly-p-xyleneglycolbiscarbonate, poly-dihydroxydiphenyl-methane carbonate,poly-dihydroxydiphenylethane propane carbonate, andpoly-dihydroxydiphenyl-l, lethane carbonate.

It is desired that the carbonyl group-containing polymer to be used inthis invention contains carbonyl groups based on functional groups offree carboxylic acids, carboxylic acid salts, carboxylic acid esters,carboxylic acid amides, carboxylic anhydrides, carbonic acid esters,urethane and urea, in an amount of to 1400 milliequivalents per 100 g ofthe polymer.

Such carbonyl group-containing polymers should be substantially linearand be molten at temperatures for melt molding the resulting resinouscomposition, for instance, at to 300C, preferably 180 to 250C.

Carbonyl group-containing polymers which are readily available, can beeasily blended and are very effective for improving the processabilityof the final resinous composition, that is, polymers which areespecially suitable for attaining the objects of this invention,

are polyvinyl acetate; copolymers of ethylene with a vinyl monomercontaining a carboxylic acid salt group, such as vinyl acetate/ethylenecopolymers, acrylic acid- /ethylene copolymers, ethyl acrylate/ethylenecopolymers and ionomers; and aliphatic polyamides such aspoly-m-aminocaproic acid, poly-w-aminoundecanoic acid,poly-m-aminododecanoic acid, polyhexamethylene adipamide andpolyhexamethylene sebacamide.

The molecular weight of the carbonyl groupcontaining polymer to be usedis not particularly critical, as far as it is within such range that thepolymer can be molded into a film or vessel.

In order to improve the processability of the resinous composition andthe surface smoothness of the molded structure, it is important that theresinous composition should comprise a carbonyl group-containing polymerin an amount of 0.5 to 15 parts by weight per 100 parts by weight of thesum of a polyolefin, especially a low density polyethylene, and asaponified product of an ethylene-vinyl acetate copolymer.

A resinous composition comprising a saponified product of anethylene-vinyl acetate copolymer and a polyolefin is relativelysufficient in that the composition has an excellent gas permeationresistance and a high impact resistance, but it is defective in that itis inferior in processability, namely melt-extrusion moldability, to apolyolefin or a saponified ethylene-vinyl acetate copolymer alone.Further, a molded article composed of a resinous composition of saidpolyolefin, es-

carbonate, poly-dihydroxyphenyl-Z, 2-

pecially low density polyethylene and saponified copolymer hastransparency, but it is defective in that it frequently has a crapedapperance and it lacks the surface smoothness'and uniformity.

This defect is conspicuous especially when the ethylene content of thesaponified ethylene-vinyl acetate copolymer is low and hence, thehydroxyl group concentration is high, or when the amount incorporated ofthe saponified copolymer is great in the resinous composition.

When such resinous composition comprising the polyolefin and saponifiedcopolymer is incorporated with the above-mentioned carbonylgroup-containing polymer in an amount of 0.5 to 15 parts by weight per100 parts by weight of said resinous composition, the flowability at themelt molding is generally improved by more than and the melt moldingprocessing can be facilitated greatly. Further, the surface of anarticle formed by melt molding such composition incorporated with thecarbonyl group-containing polymer is smooth and uniform, and thus, thedefect of the rough surface or craped apperance can be overcome.

The above effects of improving the processability and preventingoccurrence of the rough surface or craped apperance are conspicuous whenthe hydroxyl group concentration in the saponified ethylene-vinylacetate copolymer is relatively high, for instance, the saponitiedproduct has an ethylene content of 25 to 50 mole percent.

The above improvement is owing to the characteristic properties of thecarbonyl groupcontaining polymer, and it is difficult to improve theprocessability by incorporation of other polymers. For instance, asillustrated in Comparative Examples given hereinbelow, incorporation ofsuch polymers as polypropylene, polystyrene, polyisobutylene andstyrene-butadiene copolymers into a resinous composition comprising alow density polyethylene and a saponified product of an ethylene-vinylacetate copolymer hardly improves the melt-moldability of thecomposition in general.

An especially preferable amount incorporated of the carbonylgroup-containing polymer varies considerably depending on the kind andcarbonyl group concentration of the carbonyl group-containing polymer,and the hydroxyl group concentration and amount incorporated of thesaponified ethylene-vinyl acetate copolymer.

In this invention, an especially preferable resinous compositionconsists essentially of:

A. 30 to 98 by weight of a low density polyethylene having a density of0.917 to 929 g/cc,

B. 2 to 70 by weight of a saponified product of an ethylene-vinylacetate copolymer having an ethylene content of 25 to 50 mole percentand a saponification degree of at least 99 and C. 3.0 to 15.0 parts byweight, per 100 parts by weight of the sum of (A') and (B'), of acarbonyl group-containing polymer having a carbonyl group concentrationof 1.5 to 12.0 m.eq/g.

In the molded structure having the novel specific layer distributionaccording to this invention, it is important that the molded structureshould be molded from a molten mixture comprising (A) the abovementionedpolyolefin and (B) the above-mentioned saponified ethylene-vinyl acetatecopolymer at a weight ratio of A B ranging from 95 5 to 75 25,especially from 95 5 to 80 20, and 0.5 to parts by weight,

per parts by weight of the sum of (A) and (B), of a carbonylgroup-containing polymer. In this embodi ment of this invention, bymaintaining the mixing ratio of the polyolefin (A) and the saponifiedethylene-vinyl acetate copolymer (B) within the above-mentioned range,it is made possible to obtain a molded structure having a specificmulti-layer structure in which the polymer composition is different inthe thickness direc tion but substantially identical in theplanedirection, and the layers are continuous with respect to the planedirection. For instance, when the ratio ofthe saponified ethylene-vinylacetate copolymer in the molten mixture is less than 5 by weight orgreater than 25 by weight, it is difficult to form definitely in theresulting molded structure (a) layers which contain predominantly thesaponified ethylene-vinyl acetate copolymer, that is, layers whichcontain said saponified copolymer in an amount expressed by the formulaM m X (in which m is a number of from 1.2 to 4) and (b) layers whichcontain predominantly the polyolefin, that is, layers which contain thesaponified copolymer in an amount expressed by the formula M m X (inwhich m is a number of from 0 to 0.9). Further, in either of the abovetwo cases, it is difficult to maintain both the permeability of oxygenand carbon dioxide gas and the permeability of water vaporcoincidentally at desired levels.

The mixing of the polyolefin, saponified ethylenevinyl acetate copolymerand carbonyl group-containing polymer may be accomplished by a methodknown per se, and any particular limitation is not imposed on the mixingmethod. Namely, it is sufficient to blend the polyolefin, saponifiedethylene-vinyl acetate copolymer and carbonyl group-containing polymerin the powdery or granular state at room temperature by means of a mixeror the like prior to the melt molding operation, and an operation ofmixing them in the molten state is not especially required. However, ifdesired, they are melt-blended by means of a customary pelletizer or thelike.

The resinous composition of this invention may further comprise otherpolymers, for instance, other polya-olefins, olerin copolymers, vinylpolymers, diolefin polymers and olefin-vinyl-type copolymers, in suchamounts as will not give substantially any bad influences to the gaspermeation resistance, impact resistance and transparency of theresulting composition, for instance, in amounts of up to 10.0 parts byweight per 100 parts by weight of the composition.

In the preparation of the resinous composition of this invention, whenthe final product is used as a packaging material for foodstuffs, it ispreferable to conduct the preparation without use of so calledadditives. However, if desired, it is possible to incorporate knownadditives such as ultraviolet absorbents, stabilizers, lubricants,pigments and antistatic agents.

Molding Process The resinous composition of this invention may be moldedinto optional molded articles such as films, sheets, tubes, bottles andtanks by a melt-molding method known per se, for instance, a methodemploying a melt-extruder. The melt extrusion temperature adopted duringthe molding operation differs depending on such factors as theproperties of the extruder used, the molecular weights and mixing ratiosof the resins, the ethylene content of the saponified copolymer, andthekind and molecular weight of the carbonyl group-containingthermoplastic polymer. In general, it

The novel molded structure of the specific layer distribution accordingto this invention can be usually formed by melting the above-mentionedresinous composition in the blended state, and extrusion molding themolten mixture (i) at a temperature of 170 to 250C., (ii) under apressure of 10 to 300 Kg/cm and (iii) under such extrusion conditionthat the difference between the average flow rate (V,) of the melt ofsaid polyolefin and the average flow rate (V of said ethylene-vinylacetate copolymer saponified product is at least 1 cm/sec.

According to this preferable method of this invention, by conducting themolding so that the above three conditions (i), (ii) and (iii) will besatisfied, it is possible to form both layers (a) in which thesaponified ethylene-vinyl acetate copolymer is predominantly containedand layers (b) in which the polyolefin is predominantly contained, in aflow of the resin melt coming out of the die head of the extruder.

In case the extrusion molding temperature is lower than 170C., since themolding temperature approximates the melting point of the saponifiedethylene-vinyl acetate copolymer, in the resulting molded product it isimpossible to attain a layer structure in which layers are continuouswith respect to the plane direction. Further, in case the extrusionmolding temperature is higher than 250C, the molten resin flows areintermingled too closely and it is difficult to obtain a molded producthaving the specific multi-layer structure specified in this invention,and degradation is caused by oxidation or thermal decomposition of theresins, especially the saponified ethylene-vinyl acetate copolymer.

At an extrusion molding pressure lower than 10 Kglcm it is difficult toattain the average flow rate difference of at least 1 cm/sec between theaverage flow rate (2,) of the polyolefin melt and the average flow rate(V of the saponified copolymer melt. On the other hand, at an extrusionmolding pressure exceeding 300 Kglcm intermingling of the resin flows isbrought about and it is difficult to form the specific multilayerstructure in the resulting molding structure.

In this invention, it is especially important that the extrusionconditions are so selected that the value expressed by the followingformula lw-lv-l A v is at least 1 cm/sec, preferably 1 to 10 cm/sec. Inthe instant specification and claims, the average flow rate (V) isdefined to be the value expressed by the following formula wherein Qstands for the amount (Kg/hr) ofthe resin melt extruded from the die ofthe extruder at prescribed temperature and pressure, d designates thedensity (g/cc) of the resin melt and R represents the radius (cm) of thedie passage. The density of the resin melt can be determined bycalculating the amount extruded 1; (cc) at prescribed pressure (e.g.,Kg/cm and temperature by means of, for instance, a viscometer of theconstant pressure extrusion type according to the following equation 1HA rrr l wherein H is the length (cm) of the lowering of the plunger, Ais the cross-sectional area (cm of the barrel, r is the orifice radius(cm) and l is the orifice length (cm), measuring the weight W (g) of *1cc of the extrudate, and conducting the calculation according to thefollowing formula d W/n (g/cc) In this invention, conditions foradjusting the AV value to at least 1 cm/sec are attained, for instance,by the following procedures: t

1. With use of a melt extruder of the same structur and capacity, thedegree of dependency of the average flow rate on temperature andpressure is determined with respect to each of the starting polyolefinand saponified copolymer, respectively, and the temperature and pressureconditions are decided so that the difference (AV) between the averageflow rate (V of the polyolefin melt and the average flow rate (V of thesaponified copolymer melt will be at least 1 cm/sec.

2. The structure or dimention of the extruder is changed or modified sothat under prescribed temperature and pressure conditions the value AVwill be at least 1 cm/sec. For instance, since the radius of a passagefor the resin melt in the die of the extruder gives a great influence tothe flow rate of the resin melt, the condition of the value V being atleast 1 cm/sec is attainable by adjusting the radius of the abovepassage within a suitable range.

3. It is possible to satisfy the condition of the AVvalue being at least1 cm/sec by combining the above procedures (l) and (2) appropriately.

In conducting the molding method of this invention, if under suchconditions as will give the AV value of less than 1 cm/sec, it isdifficult to obtain a molded structure having the specific multi-layerstructure specified in this invention. On the other hand, when the AVvalue is too great, a good balance is not obtained between the flows ofthe molten polyolefin and of the molten saponified copolymer and hence,the molding tends to be difficult in some cases. In view of theforegoing, it is desired to select such conditions as will give the AVvalue ranging from I to 10 cm/sec.

As far as the above condition is satisfied, any of known melt extrudersmay be optionally used in this invention. As such extruder there may bementioned an extruder comprising a cylinder zone constructed of apassage equipped with a rotary screw and a resinfeeding openingconnected with said passage; a die provided with a passage connectedwith said passage of the cylinder zone; and a die head provided with anextrusion opening attached to the end point of said die and connectedwith the die passage. It is important that care must be taken so thatthe resin melt formed in the cylinder zone of the extruder is allowed tomove through passages of the die and die head in the form of a laminarflow. In other words, it is important that substantial mingling ofmolten resin flows is not caused to occur. Accordingly, it is preferredto employ as the screw a full-flighted screw such as a metering screw,but in the case of an ordinary screw generally called a mixing screw,such as a screw of the Dulmade type, if it has five or less threads inthe mixing zone, it is possible to obtain a molded structure having thespecific multi-layer structure specified in this invention by suitablychoosing the extrusion conditions of such screw, for instance, thediameter of the screw or the radius R of the die passage. In order toincrease the effect of kneading or mixing resins, or to preventincorporation of foreign substances into a molded article, such membersas a breaker plate and a screen are mounted at the die portion of theextruder in some cases in the art of the extrusion molding. In thisinvention, however, provision of such members on the die portion is notpreferred because it prevents the molten resins from flowing in thelaminar form. But if desired, it is permissible to use a breaker platehaving less than 300 holes, or less than 5 screens of 120 mesh, and insuch case, if the provision place of such breaker plate or screens, theradius R of the die passage, or other extrusion condition is suitablyadjusted, it is possible to obtain a molded structure having themulti-layer structure specified in this invention. Furthermore, in casethe AV value is within the above-mentioned range but relatively small,by employing an extruder having a die passage of a relatively greatlength, it is made possible to manifest the above-mentioned specificlayer structure more prominently and conspicuously in the resultingmolded structure.

As the die head, any of a T-die head (or a slit die head) used for theordinary film-forming method, a ring die head used for the inflationfilm-forming method, and a die head of the cross-head or spider typeused for formation of containers by the blow molding may be used in thisinvention.

The mixing of a polyolefin, an ethylene-vinyl acetate copolymersaponitied product and a carbonyl groupcontaining thermoplastic polymermay be carried out according to an optional method known per se, and themethod for the primary mixing is not particularly critical in thisinvention. That is, it is sufficient to mix the polyolefin, thesaponified copolymer and the carbonyl group-containing polymer in thepowdery or granular state at room temperature merely by means of a mixeror the like prior to the melt molding, and any operation of mixing themin the molten state is not especially required. However, it is possibleto employ a mixture which has once been molten and blended, such asflashes or fins formed during the molding operation.

The operational procedures for molding the composition of this inventioninto films, sheets, containers, tubes, pipes and the like are well knownin the art except for the above-mentioned points. Therefore, any specialdescription is not given to these known procedures in the instantspecification. These procedures for the molding operation are detailedin, for instance, the following literature references:

Keiji Oshima and Shoji Seto; Methods of Molding and Processing SyntheticResins l-Iigh Polymer Publishing Co., Inc., Kyoto (1956); Keiji Sawada;Extrusion Molding of Plastics and Its Application Seibundo Shinkosha,Tokyo (1966);

David A. Jones and Thomas W. Mullen; Blow Molding Rheinhold, New York(1961); and Gerhard Schenkel; Plastics Extrusion Technology and TheoryAmerican Elsevier Publishing Co., Inc., New York (1966).

Structure of Molded Product The molded product of this invention has, ingeneral, a thickness of more than 60 t, especially from 150 [.L to 6 mm,and is useful as a moldedstructure having twoor three-dimensionalplanes. Such molded structure includes films, sheets, embossed sheets,tubes, pipes and containers such as bags, bottles and tanks.

A preferable molded structure of this invention has a specificmulti-layer structure characterized in that the polymer composition isdifferent in the thickness direction but substantially identical in theplane direction and layers are continuous with respect to the planedirection. It has heretofore been known to obtain fibrillatedfiber-like, tape-like or film-like molded articles by mixing two or morethermosplastic polymers having no compatibility with each other, meltextruding the mixture, cooling and solidifying the extrudate and drawingthe solidified extrudate (see, for instance, Japanese PatentPublications No. 9651/60 and No. 5212/64). In molded articles obtainedby these known methods, two or more thermoplastic polymers are presentin the form of independent phases where the mingling of the polymers isnot at all observed, and the peeling strength at the interfacial planebetween the adjacent phases is substantially zero. Further, at least oneof two or more of such phases tends to form a discontinuous, dispersedphase. Even if both phases are present in the continuous form, it isdifficult to obtain a molded structure in which both phases arecontinuous with respect to the plane direction. r

In contrast, according to a preferable embodiment of this invention, itis possible to obtain a molded structure having the above-mentionedspecific multilayer structure by selecting (A) a polyolefin as one resinand (B) a saponified product of an ethylene-vinyl acetate copolymer asthe other resin, mixing them at a weight ratio of A B ranging from 95 5to 25, incorporating therein a carbonyl group-containing thermoplasticpolymer, and subjecting the mixture to the melt extrusion molding underthe above-mentioned specific extrusion and molding conditions.

It can be confirmed by various experiments that a preferable moldedstructure of this invention is characterized in that the polymercomposition is different in the thickness direction but substantiallyidentical in the plane direction and each of the layers is continuouswith respect to the plane direction.

For better illustration of this invention, description will now be madeby reference to the accompanying drawings wherein:

FIG. 1 is an electron-microscopic photo showing the cross-section in thethickness direction of a molded structure of this invention;

FIG. 2 is an electron-microscopic photo showing the cross-section in theplane direction of a molded structure of this invention;

FIG. 3 is a curve illustrating the method for determining lo and Ivalues at a wavelength of 3320 cm from the infrared absorption spectrum;

FIG. 4 is a graph illustrating one example of the calibration curve forcalculating the concentration of the saponified ethylene-vinyl acetatecopolymer present in each layer of a molded structure of this invention;

FIG. 5 is a graph illustrating the infrared absorption spectrum of eachlayer of a molded structure of this invention;

FIG. 6 is a diagramatical graph illustrating the distribution of thesaponified ethylene-vinyl acetate copolymer in the thickness directionin a molded structure of this invention; and

FIGS. 7-A and 7-B are views illustrating the method for collectingsamples in Examples of the instant specification, FIG. 7A being a topview of samples to be collected (A, B, C and D), and FIG. 7-B being aview illustrating the cross-section of the sample to be divided intothree layers 1, 2 and 3.

When the cross-section in the thickness direction and plane direction ofa preferably molded article of this invention is observed under anelectron microscope, the presence of a layer structure extendingcontinuously in the plane direction can readily be confirmed. FIGS. 1and 2 are electron-microscopic photos showing the cross-sections in thethickness and plane directions of the body portion of a bottle preparedby the method described in Example 19 given hereinbelow. In FIG. 1, theupper striped portion is of the saponified ethylene-vinyl acetatecopolymer and the sea-like" portion seen in the lower part of the photois of the low density polyethylene. From the measurement of the infraredabsorption spectrum, which will be described hereinbelow, it wasconfirmed that insular portions scattered throughout the layer structureare of the carbonyl group-containing thermoplastic polymer(ethylene-vinyl acetate copolymer in this embodiment). In FIG. 2, it isseen that in the plane direction the saponified ethylene-vinyl acetatecopolymer is not present in the striped form but in the plane-like form(namely, in the continuous phase).

Electron-microscopic photos were taken by the following method:

i. The sample was cut in a prescribed size in either the thickness orplane direction by means of a diamond knife.

ii. A small amount of gold was vacuum-plated. on

each cut face (i.e., face to be observed).

iii. Each face to be observed was enlarged by a scanning electronmicroscope and photographed. The magnification was I in FIG. 1 and 300in FIG. 2.

In FIG. 1, the vertical direction in the photo is the thicknessdirection of the body portion of the bottle (the upper part correspondsto the outer side of the bottle and the lower part corresponds to theinner side of the bottle), and the horizontal direction in the photo isthe direction vertical to the resin flow direction. In FIG. 2 thevertical direction in the photo is the direction parallel to the resinflow direction and the horizontal direction in the photo is thedirection vertical to the resin flow direction.

The fact that in the molded structure the resins are distributed so thatthe polymer composition is different in the thickness direction can beconfirmed by taking out an optional layer from the molded structure bymechanical peeling means or the like and examining the infraredabsorption spectrum of the sample. For instance, the saponifiedethylene-vinyl acetate copolymer exhibits an absorption at 3320 cm owingto the presence of the hydroxyl group, and therefore, the concentrationof the saponified copolymer present in an optional layer of the moldedstructure can be determined by the following method:

i. One polyolefin (A) and a saponified product of an ethylene-vinylacetate copolymer (B) whose ethylene content and degree ofsaponification were known were preliminarily blended (dry-blended) at aweight ratio of A B ranging from 97.5 2.5 to 30 70, and then, the meltblending was conducted at 220C. in a nitrogen atmosphere for 15 minuteswith use of a Banbury mixer (the rotation rate of the rotor being 45rpm). As a result of the microscopic observation, it was confirmed thatin all of the mixtures obtained under such conditions the components Aand B were mixed homogeneously.

ii. Each of the so formed mixture was heated at 195C. under a pressureof 10 Kg/cm to 300 Kg/cm for 2 minutes by employing a high pressurepress and formed into a film having a thickness of 5 to [.L.

iii. The infrared absorption curve of each of the so formed films wasobtained under conditions of a temperature of 20C. and a relativehumidity of 40 by means of an infrared spectrophotometer.

iv. In each infrared absorption curve thus obtained, the point at 3100cm was connected with the point at 3640 cm by a line as diagramaticallyillustrated in FIG. 3. As illustrated in FIG. 3, the values of I0 and Iwere read from the crossing point of said line and the line vertical tothe wavelength axis at 3320 cm and from the crossing point of saidvertical line and the absorption curve, respectively.

v. According to the following known equation wherein I is the averagethickness (u) of the film used for the infrared absorption measurement,C designates the concentration (percent by weight) of the saponifiedethylene-vinyl acetate copolymer, and K is a constant, the values of(log(lo/l) [E and C were plotted to obtain the calibration curve. FIG. 4illustrates an instance of such calibration curve obtained in themixture system of a low density polyethylene (1A) having a density of0.920 g/cc (determined according to ASTM D-lSOl and a saponified productof an ethylene-vinyl acetate copolymer (18) having an ethylene contentof 25.4 mole percent and a degree of saponification of 99.2 From FIG. 4,the calibration curve expressed by the formula was obtained with respectto the mixture system of above components 1A and 1B. In the same manneras described above, the calibration curve expressed by the formula wasobtained with respect to the mixture system of a high densitypolyethylene (2A) having a density of 0.945 g/cc (determined accordingto ASTM D- 1505) and said saponified copolymer (1B). Similarly thecalibration curve expressed by the formula was obtained with respect tothe mixture system of an isotactic polypropylene (3A) having a densityof 0.914 g/cc (determined according to ASTM-ISOS) and said saponifiedcopolymer (1B). Similarly, the calibration curve expressed by theformula log (Io/[HI (0.70 X l )C was obtained with respect to themixture system of said low density polyethylene (1A) and a saponifiedethylene-vinyl acetate copolymer (2B) having an ethylene content of 30.5mole and a degree of saponification of 98.1 Still further, thecalibration curve expressed by the formula was obtained with respect tothe mixture system of the low density polyethylene (1A) and a saponifiedethylene-vinyl acetate copolymer (3B) having an ethylene content of 49.4 mole percent and a degree of saponification of 96.3 As the carbonylgroupcontaining thermoplastic polymer, there were chosen Surlyn A of theNa type having a carboxylic acid concentration of 5 mole percent, SurlynA of the Zn type having a carboxylic acid concentration of mole percent,an ethylene-vinyl acetate copolymer having a vinyl acetate concentrationof 10 by weight and an ethylene-ethyl acrylate copolymer having an ethylacrylate concentration of 18 by weight, and these polymers were moldedinto films in the same manner as described in (ii) above. Then, theirinfrared abosrption spectrum curves were obtained in the same manner asdescribed in (iii) above but in any of them there was not observed anyabsorption at 3320 cm".

vi. Parts, detailed in Examples given hereinbelow, of a molded articleobtained according to the method of this invention were divided intothree layers in the thickness direction according to the sampling methoddescribed herein below, and each layer was molded into a film by themethod described in (ii) above.

vii. The infrared absorption curve of each layer obtained in (vi) abovewas obtained under the same conditions with use of the same apparatus asin (iii) above. In FIG. 5 are illustrated infrared absorption curves ofthe layers obtained by dividing the body portion of a bottle prepared bythe method detailed in Example 19 given hereinbelow, into three layersin the thickness direction. In FIG. 5 the solid line indicates theinfrared absorption curve of the first layer, the dotted line indicatesthat of the second layer and the chain line indicates that of the thirdlayer.

viii. With respect to each of the so obtained infrared absorptioncurves, the values I0 and I were determined from the absorption at 3320cm in the same manner as in (iv) above, and from these I0 and I valuesand the average thickness (E) of each film, the value of (log(Io/I) )/;7was calculated. The calculated value was put into the calibration curveequation of the corresponding mixture system described in (v) above, andthe concentration of the saponified ethylene-vinyl acetate copolymer wascalculated.

When a molded structure of this invention is divided into three layersin the thickness direction, (a) at least one layer contains thesaponified ethylene-vinyl acetate copolymer in an amount greater thanthe average content (X), namely in an amount expressed by the formula Mm X (in which m is a number ranging from 1.2 to 4), and (b) at least onelayer contains the saponified copolymer in an amount less than the"average content (X), namely in an amount expressed by the formula M m X(in which m is a number ranging from 0 to 0.9).

The layer (a) in which the saponified ethylene-vinyl acetate copolymeris predominantly distributed may by present in either one or both of thesurface layers of the molded structure, or in the form of anintermediate layer. FIG. 6 is a view illustrating diagramatically thedistribution in the thickness direction of the saponified ethylene-vinylacetate copolymer in a molded structure of this invention, wherein theordinate indicates the ratio of the content of the saponified copolymerat an optional point in the thickness direction to the average contentof the saponified copolymer, and the abscissa indicates the dimention inthe thickness direction of the molded structure. The curve A is of amolded structure in which the saponified copolymer is predominantlydistributed in both surface layers, the curve B is of a molded structurein which the saponified copolymer is predominantly distributed in theintermediate layer, and the curves C and D are of molded structures inwhich the saponified copolymer is predominantly distributed in either ofthe surface layers.

Such four types of the distribution of the saponified ethylene-vinylacetate copolymer may be formed, for instance, by choosing and combiningappropriately the average flow rate of the polyolefin melt, the averageflow rate of the melt of the ethylene-vinyl acetate copolymer saponifiedproduct and the conditions of the melt extrusion of the resinouscomposition.

For instance, when the combination of both resins or extrusionconditions are so chosen that the average flow rate of the polyolefinmelt is higher than the average flow rate of the saponified copolymermelt, and when the molding is conducted with use of a die head in whichthe melt is not divided, such as a slit die head, the resulting sheet orfilm is characterized by the saponified copolymer distribution in thethickness direction such as shown by curve A in FIG. 6. A sheet or filmmolded under such extrusion conditions or with such combination of bothresins that the average flow rate of the polyolefin melt is lower thanthat of the saponified copolymer melt, with use of a die head in whichthe melt is not divided, such as a slit die head, is character ized bythe saponified copolymer distribution in the thickness direction such asshown by curve B in FIG. 6. Under such extrusion conditions or with suchcombination of both resins that the saponified copolymer distribution ofcurve A or B is obtained as a mentioned above, if a pipe, tube, bottle,tank or film is molded with use ofa die head in which the melt isdivided, such as a spider type die head, the resulting molded structureexhibits such a curve of the saponified copolymer content as curve C orD in FIG. 6. Even when there is used a die head in which the melt isdivided, such asa spider type die head, a molded pipe, tube, bottle,tank or film whose curve of the saponified copolymer distribution in thethickness direction is such as curve A or B can be obtained by makingthe die land portion of such die longer.

A preferable molded structure of this invention can clearly bedistinguished from a blend of a polyolefin and an ethylene-vinyl acetatecopolymer saponified and a laminated structure formed from a polyolefinand an ethylene'vinyl acetate copolymer saponified product. In a moldedstructure obtained by laminating a layer of a polyolefin and a layer ofa saponified ethylene-vinyl acetate copolymer, since there is nobondability between two resins, it is necessary to bond both the layerswith an aid of an especial adhesive. Such laminated structure may beexcellent in the gas permeation resistance, but defects are broughtabout with respect to the peel strength, heat resistance, waterresistance, hot water resistance, impact resistance and otherproperties. A molded structure composed of a homogeneous blend of apolyolefin and a saponified product of an ethylene-vinyl acetatecopolymer tends to exhibit values of the oxygen permeation resistance,carbon dioxide gas permeation resistance and water vapor permeationresistance, each of which approximates the arithmetic mean of the valuesof a molded structure of the polyolefin alone and of a molded structureof the saponified copolymer alone.

In contrast, in a preferable molded structure of this invention, a layerof a low permeability of a gas such as oxygen or carbon dioxide gas inwhich a saponified ethylene-vinyl acetate copolymer is predominantlydistributed and a layer of a high water vapor permeation resistance inwhich a polyolefin is predominantly distributed are tightly andintegrally bonded without any interfacial adhesive layer. By dint ofthis structural characteristics, the preferable molded article of thisinvention can possess a permeation resistance against oxygen, carbondioxide gas and water vapor, which is almost comparable to that of alaminated structure of a polyolefin and a saponified ethylene-vinylacetate copolymer, and mechanical properties such as peel strength andimpact resistance, almost comparable to those of a molded structure of ablend of a polyolefin and a saponified ethylene-vinyl acetate copolymer.

Thus, the molded structure of this invention in the form of a film or afilm laminated with a film of other synthetic resin or a metal foil isuseful as a film container for preserving foodstuffs, medicines, etc.for a long period of time, and when molded in the form of a tube, bag,bottle or tank, the molded structure of this invention is useful as avessel or container for preserving foodstuffs, medicines, etc.

This invention will now be illustrated in more detail by reference toExamples.

In each of Examples 14 to 27, each of sample layers was collected by thefollowing sampling method.

i. A disc of a diameter of 7.0 cm was taken from a prescribed portion(indicated in each Example) of the molded article, and the oxygenpermeability was determined.

ii. The disc-like sample after the oxygen permeability test was dried invacuo at 50C.

iii. The dried disc-like sample was cut into four rectangularparallelopipeds A, B, C and D as illustrated in FIG. 7A.

iv. Each of the four samples was divided into 3 layers in the thicknessdirection (i.e., the direction parallel to the plane) (see FIG. 7-B).

The three layers were designated as follows:

a. In case the molded article was sheet:

layer 1 surface portion closely contacted with a take-up roll layer 2intermediate portion layer 3 surface portion not contacted with atake-up roll b. In case the molded article was a film bottle or pipeformed by inflation molding: layer 1 portion corresponding to the outerpor tion of form of the molded article before cutting (outside portionof the cylindrical form) layer 2 intermediate portion layer 3 portioncorresponding to the inner portion of the form of the molded articlebefore cutting (inside portion of the cylindrical form) Accordingly,when the values of the saponified ethylene-vinyl acetate copolymerconcentration (content) given with respect to layers 1, 2 and 3 of thesame alphabetic letter (one of A, B, C and D) are compared in Tablesgiven in Examples, it is possible to know the concentration differencein the thickness direction of the molded article. Further, when thevalues of the saponified copolymer concentration (content) given withrespect to samples A, B, C and D of the same numerical figure (one of 1,2 and 3) are compared, it is possible to know the concentrationdifference in the plane direction of the molded article.

Abbreviations used in Tables of Examples have the following meaning:

d; density (g/cc) (determined according to ASTM D1505) of polyolefin Et;ethylene content (mole percent) of saponified ethylene-vinyl acetatecopolymer PO/EV; mixing ratio (weight ratio) of polyolefin (X) tosaponified ethylenevinyl acetate copolymer (V) C; amount added (parts byweight) of carbonyl group-containing polymer Out'put; amount extrudedfrom extruder (g/min) Q0 oxygen permeability (cc/m 'day'atm200 u) QCOcarbon dioxide gas permeability (cc/m -day-atm-200 p.) QH O; water vaporpermeability (g/m -day'50 p.) E; tensile elasticity (Youngs modulus)(Kg/cm Sf; tensile strength at breakage (Kg/cm) ef; tensile distortionat breakage (percent) HAZE; haze value (percent) Nf; frequency ofbreakage (times) (the frequency of the falling test until the firstbottle is broken when 20 bottles are subjected to the falling test 50times) EXAMPLE 1 Parts by weight of a composition consisting of amixture composed of a low density polyethylene having a melt index of0.34 (measured according to ASTM D- 1238; the same. shall applyhereinafter) and a density of 0.928 (measured according to ASTM D-l505;the same shall apply hereinafter) and a saponified product of anethylene-vinyl acetate copolymer having an ethylene content of 25 molepercent and a degree of saponification of 93 at a mixing weight ratio of30 70, was incorporated with 15 parts by weight of either of thefollowing polymers as a carbonyl group-containing thermoplastic polymer(C); (a) a polyvinyl acetate obtained by the bulk polymerization, havingan intrinsic viscosity, measured at 30C. in acetone solution, of 1.53 dHg and a carbonyl concentration of l 1.6 milliequivalents per gram ofthe polymer, (b) 6 nylon having a relative viscosity in sulfuric acidsolution of 3.4 (concentration 10.0 g/l; temperature 20C.) and acarbonyl concentration of 8.9 milliequivalents per gram of the polymer,(c) Surlyn A (trademark for product of Du Pont) (ionomer of the zinctype) having a melt index of 0.7, a density of 0.960 and a carbonylcontent of 1.6 milliequivalents per gram of the polymer, (d) anethylene-vinyl acetate copolymer having an ethylene content of 83 molepercent, a melt index of 2.4 and a carbonyl concentration of 4.5milliequivalents per gram of the polymer, (e) an acrylic acid-graftedpolyethylene having an acrylic acid-grafting ratio of 8.2 a melt indexof 0.9 and a carbonyl concentration of 2.5 milliequivalents per gram ofthe polymer and (f) an ethylene-ethyl acrylate copolymer having anethylene content of 89 mole percent, a melt index of 6.2 and a carbonylconcentration of 3.1 milliequivalents per gram of the polymer. Theresulting composition was dry-blended at room temperature and moldedinto a film having a thickness of about 200 ,u. by employing an extruderequipped with a nylon type screw having a diameter of 25 mm and a lengthof 625 mm (screw rotation rate 65 rpm; die temperature 250C.) and a T-die.

For comparison, films were molded under the same extrusion moldingconditions with use of the same extrusion molding machine as describedabove, from the above-mentioned low density polyethylene; theabovementioned saponified ethylene-vinyl acetate copolymer; a 70 (weightratio) two-component mixture of the above-mentioned low densitypolyethylene and saponified ethylene-vinyl acetate copolymer; acomposition consisting of 100 parts by weight of a 30 70 (weight ratio)mixture of the above-mentioned low density polyethylene and saponifiedethylene-vinyl acetate copolymer and 15 parts by weight of an isotacticpolypropylene having a melt index of 1.0; a composition of 100 parts ofa 30 70 (weight ratio) mixture of the above-mentioned low densitypolyethylene and saponified ethylene-vinyl acetate copolymer and 15parts by weight of a polyisobutylene having a viscosity averagemolecular weight of 1,000,000 (calculated from the intrinsic viscositymeasured at C. in tetrahydrofuran solution); a composition consisting of100 parts by weight of a 70 30 (weight ratio) mixture of theabove-mentioned low density polyethylene and saponified ethylene-vinylacetate copolymer and 15 parts by weight of an atactic polystyrenehaving a melt index of 3.5; and a composition consisting of 100 parts byweight ofa 70 30 (weight ratio) mixture of the abovementioned lowdensity polyethylene and saponified ethylene-vinyl acetate copolymer and15 parts by weight of a styrene-butadiene copolymer having a styrenecontent of 80 mole percent.

At the extrusion molding operation, the amount extruded from theextruder, out-put (g/min), was measured with respect to each sample.

With respect to each of the above-mentioned 13 films, the oxygenpermeability, Q0 (cclm day'atm-2o u), was determined at a temperature of27C. and a relative humidity of 90 by employing a gas permeabilitytester. Further, with use of a tensile tester, the tensile elasticity inthe stretch direction, E (Kg/cm), the tensile strength in the stretchdirection at breakage, Sf (Kg/cm and the tensile elongation in thestretch direction at breakage, ef (percent), were measured at atemperature of 20C., a relative humidity of and a stretch rate of 300mm/min. The appearance of each film was evaluated based on the visualobservation made by 25 men. The evaluation score of the appearance ofthe film from the saponified ethylene-vinyl acetate copolymer having thebest appearance and the evaluation score of the appearance of the filmfrom the above-mentioned twocomponent mixture having the worstappearance were precribed as +5 and 0, respectively. The appearance ofeach of other films was compared with those of these standard films andthe relative score of the film was determined by each of 25 men. Theappearance score was an average of the scores determined by 25 men.

Each of the films was pressed under a pressure of Kg/cm at 250C. for 10minutes by means of a high pressure press to form a thin film having athickness of 50 i 3 u, and with respect to the so formed thin film, thewater vapor permeability, QH O (g/m-day-atm50 p.) was determinedaccording to the method JlS Z- 1208, and the haze value, HAZE (percent)was measured by employing a haze tester at a temperature of 20C. and arelative humidity of 65 The amount extruded (out-put), oxygenpermeability (Q0 water vapor permeability (QH O), tensile elasticity(E), tensile strength at breakage (Sf), tensile elongation at breakage(ef), haze value (HAZE) and appearance condition (appearance) of eachfilm are shown in Table 1.

From the date shown in Table l,-the following m atters can be seen:

Compositions formed by incorporating into the twocomponent mixture ofthe low density polyethylene and saponified ethylene-vinyl acetatecopolymer, as a carbonyl group-containing thermoplastic polymer (C),polyvinyl acetate (PVAC in Table 1), 6-nyloit (6-Nylon in Table l),Surlyn A (trademark) (Surlyn-A in Table 1), ethylene-vinyl acetatecopolymer (EVA in Table l), acrylic acid-grafted polyethylene (AG-PE inTable 1) or ethylene-ethyl acrylate copolymer (EEA in Table l) werecomparable to the above-mentioned twocomponent mixture with respect tothe oxygen permeability, water vapor permeability, tensile elasticityand haze value, and in films of these compositions the amount extrudedand tensile elongation at breakage were improved over the film of thetwo-component mixture. Further, the appearance of each of films formedfrom these compositions was improved and was almost comparable to thatof the film formed from the saponified ethylene-vinyl acetate copolymer.ln compositions obtained by incorporating as a third component (C)polypropylene (PP in Table 1), polyisobutylene (PIB in Table l),polystyrene (PS in Table l) or styrenebutadiene copolymer (SBR), suchimprovements as mentioned above were hardly observed.

Table, l

LDPE/EV Polymer C Amount Out- (parts put 00, QH,O E Sf sf HAZEAppearance weight) Kind TABLE I-Continued LDPE/EV Polymer C Amount Out-(ptarts put Q QHzO E Sf ef HAZE Appearance weight) Kind 30/70 PP 62.714.6 42.9 15500 196 300 25.3 +0.7 30/70 15 NB 59.4 17.2 47.0 14600 205750 23.9 +1.6 30/70 15 P8 58.0 27.6 52.4 16300 140 80 79.2 -O.4 30/70 15SBR 59.6 26.5 50.6 15100 162 250 70.5 +0.1 30/70 15 PV Ac 80.3 10.7 46.014500 210 800 24.0 +3.3 30/70 15 6 Nylon 81.5 10.1 44.6 14600 216 80023.1 +4.0 30/70 15 Surlyn A 82.6 10.2 45.0 14000 213 800 23.2 +4.5 30/7015 EVA 84.5 10.6 45.3 14500 212 850 22.6 +4.7 30/70 15 AG PE 85.0 10.446.0 14900 215 800 25.0 +3.6 30/70 15 EEA 84.3 10.8 44.2 14300 211 85024.6 +4.4 0/100 0 87.7 5.6 145 19500 300 200 215 +5 EXAMPLE 2 (Kg/cmtensile strength at breakage, Sf (Kg/cm A low density polyethylenehaving a melt index of 2.1 and a density of 0.917 was blended with asaponified product of an ethylene-vinyl acetate copolymer having anethylene content of mole percent and a degree of saponification of 93 ata mixing weight ratio indicated in Table 2, and 100 parts by weight ofthe resulting composition was incorporated with 0 25.0 parts by weightof 6-nylon having a carbonyl group concen- 25 tration of 8.9milliequivalents per gram of the polymer and a relative viscosity,measured in 98 sulfuric acid containing the polymer at a concentrationof 10.0 g/l at 20C., of 3.4. Then, the composition was dryblended atroom temperature. Thirty films indicated in Table 2 were molded fromcompositions obtained in the above manner under the same extrusionconditions with use of the same extrusion molding apparatus as describedin Example 1. Each film had a thickness of about 200 p..

The amount extruded, out-put (g/min), of each composition, and theoxygen permeability, QO (cc/m day-atm-ZOO u), water vapor permeability,QH O (g/m"day'50 1.), carbon dioxide gas permeability,

QCO (cc/m -day'atm-20O u), tensile elasticity, E 40 tensile elongationat breakage, ef (percent), haze value, HAZE (percent), and appearancecondition, appearance (point), of each film were measured. The carbondioxide gas permeability was determined at at temperature of 27C. and arelative humidity of with use of a gas permeability tester. Otherproperties were determined under the same measuring conditions accordingto the same measuring methods as in Example 1. Results are shown inTable 2.

From the results shown in Table 2, it can readily be understood that atthe mixing ratios of the low density polyethylene and saponifiedethylene-vinyl acetate copolymers ranging from 98 2 to 30 70 and at theamounts added of the nylon-6 ranging from 0.1 to 15.0 parts, the amountextruded of the composition, and the tensile elongation at breakage andappearance condition of the resulting film can be highly improved as 35compared with the case of the two-component system composition (theamount added of the nylon-6 being zero) without substantial degradationof such properties as oxygen permeability, carbon dioxide gaspermeability, water vapor permeability, tensile elasticity and hazevalue.

Table 2 LDPE/EV C Out- Q0: QCO, QH 0 E Sf ef HAZE Appearance put EXAMPLE3 A low density polyethylene having a melt index of 2.1 and a density of0.917 was mixed with a saponified product of an ethylene-vinyl acetatecopolymer having EXAMPLE 4 A low density polyethylene having a meltindex of 0.3 and a density of 0.928 was mixed with a saponified productof an ethylene-vinyl acetate copolymer having an ethylene content of 75mole percent and a degree an ethylene content of 25 mole percent and adegree of saponification of 93 at a weight ratio indicated in ofsaponification of 93 at a mixing weight ratio indi- Table 3. Then 100parts by weight of the mixture was cated in Table 4, and 100 parts byweight of the mixincorporated with 0 to 25.0 parts by weight of Surlynture was incorporated with 0 to 25.0 parts by weight of A (trademark;ionomer of the Zn ion type manufacl 0 an ethylene-vinyl acetatecopolymer having a carbonyl tured by Du Pont, U.S.A. and having a meltindex of group concentration of4.5 milliequivalents per gram of 0.7 anda density of 0.960) having a carbonyl group polymer, an ethylene contentof 83 mole percent and concentration of 1.6 milliequivalents per gram ofthe a melt indfiX 0 T e e u t ng composition as drypolymer, and thecomposition was dry-blended at ro m blended at room temperature. Thirtyfilms indicated in temperature. Thirty films indicated in Table 3 wereTable 4 were molded from Compositions formed h a molded fromcompositions f r d i a manner as d manner as described above under thesame extruslon scribed above under the same extrusion conditions witheohdmohs W1th use of the same extrusion Theldlhg P' use of the sameextrusion-molding apparatus as de- Parstus as Example 1r Each fihh h athickness of scribed in Example 1. Each film had a thickness or about 1Propertles Such asmemwned m amp about 200 p propel-ties as mentioned inExample 2 2O 2 were measured under the same measuring conditions weredetermined under the same measuring conditions aeeol'dlhg to the samemeasuring methods as Examaccording to the same measuring methods as inExam- P Results are show" Table I 1 2 Results are Shown in Table Fromthe; results shown 1n Table 4, 1t can readlly be seen that the amountextruded of the composltlon and From the results Show" Table can read'lybe the tensile elongation at breakage and appearance conthat at h "11mgrams of the PY dition of the resulting film can be highly improved asmehtlohecl low density p y y sapohlfied compared with the case of thetwo-component system ethylene-Vinyl acetate copolymer rahglhg from 98 12 composition (the amount added of the ethylene-vinyl to Q 1 70 and atthe amounts addeq of the above acetate copolymer being zero), when themixing ratios mehhehed yh A (trademark) l'ahglhg from to of theabove-mentioned low density polyethylene and -9 Parts y welghtatheamohht extruded of the saponified ethylene-vinyl acetate copolymer arein the pos1t1on and the tenslle elongation at breakage and aprange offrom 98 2 to 30 and the amount added Peafahee Cohdltloh of the resultingfilm can be highly of the above-mentioned ethylene-vinyl acetate copoly-1mproved as compared with the case of the tw0- mer is in the range offrom 0.1 to 150 parts by weight, component system composition (theamound added of and that such improvement is attained without substan-Surlyn A (trademark) being zero) without substantial 35 tial degradationof such properties as the oxygen perdegradation of properties such asoxygen permeability, meability, carbon dioxide gas permeability, watercarbon dioxide gas permeability, water vapor permeavapor permeability,tensile elasticity, haze value and bility, tensile elasticity and hazevalue. appearance condition.

Table 3 LDPE/EV c 0ut- 002 0130 011,0 E 81 cf HAZE Appearance put efHAZE Appearance C Out- .9 9 .6 1 .3 93 .5 90 55544 44 ++MM MHMH HMHMHHHHHHHHH 22 .LLLLLL- l'm' illllllllll ll 333333333322222222222222222222000055555wlm' imH 56667088902 66670044445 3 33522 2 1111 lllll125150552025AJJ9 80089930090 04 0936284705 01 7 7 EXAMPLE 6 ef HAZEAppearance A low density polyethylene having a melt index of 2.1 and adensity of0.9l7 and another low density polyethylene having a melt indexof 0.3 and a density of 0.928 were dry-blended at room temperatureindividually with either of a saponified product of an ethylene-vinylacetate copolymer having an ethylene content of 25 mole percent and adegee of saponification of 99 and another saponified product of anethylene-vinyl acetate copolymer-having an ethylene content of 75 molepercent and a degree of saponification of 99 together with nylon-6having a relative viscosity of 3.4 (solvent 98 sulfuric acid;concentration 10.0 g/l; temperature =20C.) and a carbonyl groupconcentration of Table 5 Q0, Qco, QH,0 E

Out-

. EXAMPLE 5 This Example was conducted in order to know whether or not asimilar tendencywould be observed when Example 4 was repeated by.varying the ethylene content inthe saponitied ethylene-vinyl acetatecopolymer. Films were prepared in the same manner as in Ex- LDPE/EV cample 4 from compositions formed by mixing the same low densitypolyethylene as .used in Example I with a saponified product of anethylene-vinyl acetate copolymer having an ethylene content of molepercent and a degree of saponification of 93 at mixing ratios indicatedin Table 5. Properties of the films were measured under the sameconditions according to the same measuring methods as in Example 4.Results are shown in Table 5.

2 l l l i l l l l l l l l 0 omomlQllKZiQl 4 L4 02 Ohl6 0 0 0 0 05555555566668887 8997889900000

1. A MOLDED STRUCTURE HAVING AN IMPROVED GAS PERMEATION RESISTANCE, SAIDMOLDED STRUCTURE HAVING BEEN FORMED BY MEANS OF EXTRUSION MOLDING FROM AMOLTEN MIXTURE CONTAINING (A) A POLYOLEFIN AND (B) A SAPONIFIED PRODUCTOF AN ETHYLENEVINYL ACETATE COPOLYMER HAVING AN ETHYLENE CONTENT OF 25TO 50 MOLE PERCENT AND A DEGREE OF SAPONIFICATION OF AT LEAST 96% AT AWEIGHT RATIO OF A : B RANGING FROM 95 : 5 TO 75 : 25, AND (C) 0.5 TO 15PARTS BY WEIGHT, PER 100 PARTS BY WEIGHT OF THE SUM OF SAID POLYEFIN ANDSAID ETHYLENE-VINYL ACETATE COPOLYMER SAPONIFIED PRODUCT, OF ATHERMOPOLASTIC POLYMER CONTAINING A CARBONYL GROUP IN THE MAIN OR SIDECHAIN THEREOF, SAID MOLDED STRUCTURE HAVING A LAYER STRUCTURE IN WHICHTHE POLYMER COMPOSITION IS DIFFERENT IN THE THICKNESS DIRECTION BUTSUBSTANTIALLY IDENTICAL IN THE PLANE DIRECTION AND EVERY TWO ADJACENTLAYERS ARE BONDED TO EACH OTHER WITHOUT ANY INTERMEDIATE BONDING LAYEROF AN ADHESIVE, SAID LAYER STRUCTURE CONSISTING ESSENTIALLY OF (A) ATLEAST ONE LAYER IN WHICH THE SAPONIFIED ETHYLENE-VINYL ACETATE COPOLYMERIS PREDOMINANTLY DISTRIBUTED, (B) AT LEAST ONE LAYER IN WHICH THEPOLYOLEFIN IS PREDOMINANTLY DISTRIBUTED, AND (C) AT LEAST ONE LAYERWHICH COMPRISES THE SAPONIFIED ETHYLENE-VINYL ACETATE COPOLYMER AND THEPOLYOLEFIN IN AMOUNTS SUBSTANTIALLY SAME AS THE AVERAGE CONTENTS OF THESAPONIFIED ETHYLENE-VINYL ACETATE COPOLYMER AND THE POLYOLEFIN IN SAIDLAYER STRUCTURE, SAID LAYER (C)INTERVENING BETWEEN SAID LAYER (A) ANDLAYER (B) TO BOND THEM INTEGRALLY, THE SAID CARBONYL GROUP-CONTAININGTHERMOPLASTIC POLYMER BEING DISTRIBUTED THROUGHOUT THE SAID LAYERSTRUCTURE, AND WHEREIN WHEN SAID MOLED STRUCTURE IS DIVIDED IN THREELAYER IN THE THICKNESS DIRECTION, AT LEAST ONE LAYER (A) CONTAINS THEETHYLENE-VINYL ACETATE COPOLYMER SAPONIFIED PRODUCT IN AN AMOUNTEXPRESSED BY FOLLOWING FORMULA M1 = M1 X WHEREIN X IS THE AVERAGECONTENT (PERCENT BY WEIGHT) OF THE ETHYLENE-VINYL ACETATE COPOLYMERSAPONIFIED PRODUCT IN SAID MOLDED STRUCTURE, M1 IS A NUMBER OF FROM 1.2TO 4, AND M1 IS THE CONTENT (PERCENT BY WEIGHT) OF THE ETHYLENEVINYLACETATE COPOLYMER SAPONIFIED PRODUCT IN SAID LAYER, AND AT LEAST ONELAYER (B) CONTAINS THE ETHYLENE-VINYL ACETATE COPOLYMER SAPONIFIEDPRODUCT IN AN AMOUNT EXPRESSED BY THE FOLLOWING FORMULA M2 - M2X WHEREINX IS AS DEFINED ABOVE, M2 IS A NUMBER OF FROM 0 TO 0.9, AND M2 IS THECONTENT (PERCENT BY WEIGHT) OF THE ETHYLENE-VINYL ACETATE COPOLYMERSAPONIFIED PRODUCT IN SAID LAYER.
 2. A molded structure according toclaim 1 wherein when said molded structure is divided in three layers inthe thickness direction, a first surface layer is said layer (a), and asecond layer is said layer (b) and an intermediate layer is said layer(c).
 3. A molded structure according to claim 1 wherein when Said moldedstructure is divided in three layers in the thickness direction, twosurface layers comprise said layer (a) and an intermediate layercomprises said layer (b).
 4. A molded structure according to claim 1wherein when said molded structure is divided in three layers in thethickness direction, two surface layers comprise said layer (b) and anintermediate layer comprises said layer (a).
 5. A molded structure isset forth in claim 1, wherein the thermoplastic polymer (C) is a memberselected from the group consisting of polymers composed of a monomerexpressed by the following formula
 6. A molded structure as set forth inclaim 1, wherein the thermoplastic polymer (C) is a member selected fromthe group consisting of polymers composed of a monomer expressed by thefollowing formula
 7. A molded structure as set forth in claim 1, whereinthe thermoplastic polymer (C) is an ionomer.
 8. A molded structure asset forth in claim 1, wherein the thermoplastic polymer (C) is acopolymer of maleic anhydride with other Alpha , Beta -ethylenicallyunsaturated monomer free of a carbonyl group.
 9. A molded structure asset forth in claim 1, wherein the thermoplastic polymer (C) is apolyamide or interpolyamide consisting of the recurring units expressedby the formula
 10. A molded structure set forth in claim 1, wherein thepolyolefin is a crystalline homopolymer or copolymer of an olefinexpressed by the following formula
 11. A molded structure set forth inclaim 1, wherein the polyolefin is a low density polyethylene having adensity of from 0.917 to 0.929 g/cc.
 12. A molded structure set forth inclaim 1, wherein the polyolefin is a medium density polyethylene havinga density of from 0.930 to 0.939 g/cc.
 13. A molded structure set forthin claim 1, wherein the polyolefin is a high density polyethylene havinga density of at least 0.940 g/cc.
 14. A molded structure set forth inclaim 1, wherein the polyolefin is an isotactic polypropylene.
 15. Amolded structure set forth in claim 1, wherein the saponifiedethylene-vinyl acetate copolymer has an intrinsic viscosity ( eta ),measured at 30*C. with use of a mixed solvent of 85 % by weight ofphenol and 15 % by weight of water, of from 0.07 to 0.17 l/g.
 16. Amolded structure set forth in claim 1, wherein the thermoplastic polymer(C) contains carbonyl groups in an amount of from 120 to 1400milliequivalents per 100 g of the polymer.
 17. A molded structure setforth in claim 1, which is in the form of a container.
 18. A moldedstructure set forth in claim 1, which is in the form of a film.
 19. Amolded structure set forth in claim 1, which is in the form of a tube.20. A molded structure, said molded structure having been formed bymeans of extrusion molding from a molten mixture containing (A) apolyolefin and (B) a saponified product of an ethylene-vinyl acetatecopolymer having an ethylene content of 25 to 50 mole percent and adegree of saponification of at least 96% at a weight ratio of A : Branging from 95 : 5 to 75 : 25, and (C) 0.5 to 15 parts by weight, per100 parts by weight of the sum of said polyolefin and saidethylene-vinyl acetate copolymer saponified product, of a thermoplasticpolymer containing a carbonyl group in the main or side chain thereof,under such condition that the difference between the average flow rateof the polyolefin melt and the average flow rate of the melt of thesaponified ethylene-vinyl acetate copolymer is at least 1 cm/sec and themolten mixture moves through the extrusion apparatus in the form of alaminar flow, said molded structure having a layer structure in whichthe polymer composition is different in the thickness direction butsubstantially identical in the plane direction, said layer structureconsisting essentially of (a) at least one layer in which the saponifiedethylene-vinyl acetate copolymer is predominantly distributed, (b) atleast one layer in which the polyolefin is predominantly distributed,and (c) at least one layer which comprises a mixture of saponifiedethylene-vinyl acetate copolymer and the polyolefin in an approximatelysame amount as the average content, said layer (c) intervening betweensaid layer (a) and layer (b) to bond them integrally, the said carbonylgroup-containing thermoplastic polymer being distributed throughout thelayer structure, and wherein when said molded structure is divided inthree layers in the thickness direction, at least one layer (a) containsthe ethylene-vinyl acetate copolymer saponified product in an amountexpressed by following formula M1 m1X wherein X is the average content(percent by weight) of the ethylene-vinyl acetate copolymer saponifiedproduct in said molded structure, m1 is a number of from 1.2 to 4, andM1 is the content (percent by weight) of the ethylene-vinyl acetatecopolymer saponified product in said layer. and at least one layer (b)contains the ethylene-vinyl acetate copolymer saponified product in anamount expressed by the following formula M2 - m2X wherein X is asdefined above, m2 is a number of from 0 to 0.9, and M2 is the content(percent by weight) of the ethylene-vinyl acetate copolymer saponifiedproduct in said layer.